Doctor blade

ABSTRACT

A doctor blade, in particular for metering of inks and coatings from an engraved surface, has a flat oblong base body and a blade region with a working edge being formed at one of the longitudinal sides of the base body. The blade region is at least partially made of a plastics material, whereas the working edge is formed of the plastics material. The base body is made from a reinforced plastics material. The opposing main outer surfaces of the base body are constituted by plastic layers made from a first material, where at least one inner layer made from a second material having a higher rigidity than the first material is provided in between the plastic layers.

TECHNICAL FIELD

The invention relates to a doctor blade, in particular for metering ofinks and coatings from an engraved surface, the doctor blade having aflat oblong base body and a blade region with a working edge beingformed at one of the longitudinal sides of the base body. The inventionfurther relates to a method for manufacture of a doctor blade.

BACKGROUND ART

In the printing industry, doctor blades are used in particular for themetering of inks and coatings from an engraved surface, e.g. from thesurface of a printing cylinder: After the recessed cells of the cylinderare covered with ink, a blade must wipe away the excess ink before itreaches the printing nip. The correct application of the doctor blade iscritical in gravure and flexographic printing.

Doctor blades are consumables. They are periodically replaced. It istherefore favorable if doctor blades are cost-efficient and if theirhandling is as safe as possible.

Present day doctor blades mainly come in two forms, namely metallic andpolymeric (non-metallic). Metallic blades, usually made of carbon steel,offer the following benefits:

They have a superior rigidity in thin sections;

they are easy to manufacture even if tight tolerances have to beobserved;

they are able to support a very thin edge;

they provide clean doctoring (sharp and clean wipe);

they have a superior flatness; and

they do not exhibit any memory effects.

However, in comparison with non-metallic blades metallic blades alsohave the following negatives:

Their friction with the surface to be doctored is higher;

they are abrasive to the opposing surface;

they develop sharp edges when worn which is a point of potential danger;

they oxidize and therefore develop rust;

the debris from wear of the doctor blade contaminates the media;

they do not have any sealing properties in and of itself; and

the material is not readily available.

Consequently, non-metallic blades offer the following benefits:

Their friction with the surface to be doctored is low;

they are safer than metallic blades;

they do not develop sharp edges when worn;

they are non-abrasive;

their debris is not harmful to the media;

the material is readily available in stock;

the material has inherent sealing properties; and

there is no oxidation.

But also non-metallic doctor blades have negative properties:

They are more expensive than steel;

they have a low modulus of stiffness in thin sections which leads todeformations of the blade that hamper the precise control of thedoctoring process;

they have an inferior flatness and tend to be wavy;

they introduce additional manufacturing challenges in producing apreferred edge;

they cannot support a thin edge well;

clean doctoring is limited due to the required thickness of thematerial; and

the material retains memory.

The main reasons for using metallic blades are their rigidity andflatness. However, using metallic blades means to put up with safetyproblems as well as with abrasion to itself and the surface to bedoctored. Correspondingly, the users of non-metallic blades focus onsafety and low abrasion, putting up with low rigidity and inferiorflatness of the working edge.

Depending on the task to be performed, metallic or non-metallic doctorblades are preferred. Therefore, it has been proposed to modify bladeholders to accommodate both metallic and non-metallic blades such thatmetallic or non-metallic blades may be flexibly used subject to thespecific task to be performed.

Recent developments and designs have attempted to counter some of thenegative aspects of both types of blades by applying coatings to theblades and by manufacturing the surface of the rollers with differentmaterials (chrome and ceramic). These measures extend the life of thecomponents and enable lower friction values. Additives have also beenintroduced into the media for their properties of lubricity andprevention of oxidation.

As an example, the publication JP 4-296556 (Toppan Printing Co. Ltd.)relates to a doctor blade that is coated with a thin coating of an inkrepellent material such as silicone resin, fluorine resin, a polymercontaining a long chain acrylic group, polyolefin, alkyd resin, shellac,silicone containing fluorine, etc.

Furthermore, some doctor blade designs have been proposed that includestructural elements both made from metal as well as from a plasticsmaterial:

The DE 28 23 603 (Max Dätwyler & Co.) describes a doctor bladearrangement that comprises a metal doctor blade having a plasticcladding. The cladding constitutes outer surfaces of the doctor bladeand is firmly connected to the doctor blade in a base body region.Before the doctor blade is clamped to the doctor blade holder thecladding mainly serves as a packaging for protecting the doctor blade aswell as the user mounting the blade in the printing press. After thedoctor blade has been clamped to the doctor blade holder a removableportion of the cladding is removed in order to uncover the metallicworking edge. During operation of the doctor blade the remaining portionof the cladding serves for the damping of vibrations of the doctorblade.

U.S. Pat. No. 2,052,679 (Wainwright et al.) relates to a doctor bladefor doctoring gravure cylinders or plates. The doctor blade features aworking blade from a plastics material such as synthetic resin orcellulose derivative materials. The entire doctor blade may bemanufactured of the plastics material, whereas advantageously theplastics material is reinforced to within a short distance of theworking edge with a metal reinforcement. The metal reinforcement is ametal layer that is arranged on one of the main outer sides of theplastic blade body.

However, these designs mitigate only some specific disadvantages ofmetallic and/or non-metallic doctor blades, respectively.

SUMMARY OF THE INVENTION

It is the object of the invention to create a doctor blade pertaining tothe technical field initially mentioned that combines benefits of bothmetallic and non-metallic doctor blades while reducing or eliminatingnegative aspects of both.

The solution of the invention is specified by the features of claim 1.According to the invention the blade region is at least partially madeof a plastics material, the working edge, i.e. the region of the doctorblade that is in contact with the surface to be doctored, being formedof the plastics material, whereas the base body is made from areinforced plastics material. The opposing main outer surfaces of thebase body are constituted by plastic layers made from a first material,at least one inner layer made from a second material having a higherrigidity than the first material being provided in between said plasticlayers.

The doctor blade therefore incorporates structural components ofdifferent rigidities, whereas a plastic working edge is provided. Therigid inner layer, which may constitute a core of the doctor blade, isaccommodated in between plastics layers, the outer surfaces of thedoctor blade being constituted by the plastics material. Thereby adoctor blade is provided that is at the same time rigid andnon-abrasive. The wear debris is not harmful to the media and the doctorblade provides sealing qualities. Due to the fact that the main outersurfaces of the doctor blade are constituted by the plastics materialthe doctor blade is not subject to rusting or oxidation and the safetyfor the user is enhanced.

Preferably, the inner layer is metallic, e.g. made from steel.Alternatively, the inner layer may be manufactured from a non-metallicrigid material such as e.g. fiberglass or carbon fiber.

Preferably, a thickness of the blade region is smaller than a thicknessof the base body. This allows for providing a rigid doctor blade with aflat blade region.

Advantageously, the entire blade region is formed of the plasticsmaterial, i.e. the inner layer does not extend to the working edge butthere is a region of the doctor blade, adjacent to the working edge thatis entirely made of the plastics material. This allows for providing anon-metallic working edge that has all the advantages of knownnon-metallic working edges and that may be formed and manufactured likethe working edges of known non-metallic doctor blades.

Alternatively, the inner layer substantially extends into the region ofthe working edge, i.e. the working edge is constituted by the plasticsmaterial which is directly supported by the respective region of therigid inner layer. The blade region is designed in such a way that theworking edge is always constituted by the plastics material, even afterwear of the doctor blade.

Preferably, the inner layer is firmly adhered to the plastic layers.This enables a high rigidity as well as a high durability of the doctorblade. Due to the firm attachment all forces acting on the outer plasticsurfaces may be transmitted to the rigid base body. Alternatively, theinner layer is not attached to the plastic layers but held within theplastic layers due to the geometry of the plastic layers, i.e. theplastic layers are formed in such a way that a retaining space isformed, in which the base body is retained. It is possible tomanufacture a doctor blade that incorporates such a retaining form ofthe plastic layers as well as the firm attachment of the inner layer tothe plastic layers.

To firmly attach the inner layer to the plastic layers, these elementsare advantageously adhered together. This allows for having largeattachment surfaces between the layers and therefore for optimallydistributing the forces to be transferred from one layer to the other.Alternative attachment means may be used, such as rivets, or the plasticlayers as well as the metallic base body feature corresponding form-fitsurfaces, e.g. interacting dovetail profiles.

In a preferred embodiment of the invention, the plastic layers projectover the longitudinal side of the base body neighboring the work bladeand the projecting regions of the plastic layers are joined together.This allows to easily manufacturing a doctor blade having a plasticblade region as well as a metallic base body.

Preferably, the projecting, joined plastic layers constitute the bladeregion with the working edge. Thereby, the entire doctor blade may beessentially built up from three components, namely from an oblong rigidinner body (core) as well as from two plastic layers of the sameextension having a base area that is larger than that of the inner bodyand that are coextensively provided on both the opposing main surfacesof the inner body, in such a way that a region of the plastic layers isprojecting over the longitudinal side of the inner body. After joiningthe projecting regions of the plastic layers a blade region is formedwhere a plastic working edge may be easily formed by grinding.

Advantageously, the plastic layers consist of an oriented polyesterfilm. Corresponding films of suitable thicknesses are commerciallyavailable at comparably low costs. They are dimensionally stable,exhibit a high tensile strength and are especially well suited for beinglaminated.

Alternatively, other plastics materials are used, e.g. plasticsmaterials reinforced with fibers (such as carbon or glass fibers).

Preferentially, a thickness of each of the plastic layers amounts atleast to a thickness of the inner layer. The plastic layers are not justcoatings of the metal core but structural elements of their own. Inparticular, the thickness of each of the plastic layers is in the rangeof 0.1-0.5 mm, in particular in the range of 0.15-0.4 mm, whereas thethickness of the inner layer is in the range of 0.05-0.3 mm, inparticular in the range of 0.1-0.25 mm. These layer thicknesses allowfor the production of doctor blades that are at the same time rigid aswell as flat. If the blade region is constituted by two joined plasticlayers the given thicknesses allow for forming a working edge withoptimum operation properties for metering of inks and coatings fromengraved surfaces.

For special purposes it is possible to vary the layer thicknesses aswell as the ratios of layer thicknesses.

A doctor blade according to the invention may be manufactured by

a) providing a flat oblong core having at least one inner layer;b) arranging two plastic layers on opposing main surfaces of the core,in such a way that the plastic layers project over a longitudinal sideof the core;c) firmly adhering the plastic layers to the core;d) adhering together the plastic layers in the projecting region.

The core may be constituted by a single one-piece element having anincreased rigidity or by a composite element that comprises at least onereinforcement layer that is able to provide additional mechanicalstability to the core.

Preferably, the plastic layers and the inner layer (or the core) arelaminated together, i.e. the steps c) and d) are performed by alaminating process, i.e. an adhesive layer is provided in between thelayers and subsequently the layers are joined together using pressureand heat. This is advantageously done by running the un-laminatedmaterials through a set of heated platens, heated rollers and/or rollerswith a close heat source. Laminating is a cost-effective process thatallows for a firm attachment of neighboring layers as well as for highproduction rates.

Alternatively, spray adhesives, epoxy resins which can be spread on thesurfaces to be attached to each other or pressurized autoclavingtechniques may be used.

Other advantageous embodiments and combinations of features come outfrom the detailed description below and the totality of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings used to explain the embodiments show:

FIG. 1 A cross-sectional view of a first embodiment of a doctor bladeaccording to the invention;

FIG. 2 a cross-sectional view of a second embodiment of a doctor bladeaccording to the invention; and

FIG. 3A-C a schematic representation of an inventive method formanufacture of a doctor blade.

In the figures, the same components are given the same referencesymbols.

PREFERRED EMBODIMENTS

The FIG. 1 shows a cross-sectional view of a first embodiment of adoctor blade according to the invention, along a plane perpendicular tothe longitudinal extension of the doctor blade. The view is schematic;the dimensions are not to scale. The doctor blade 1 comprises a corebody 2 made from steel as well as two plastic layers 3, 4 arranged onboth sides of the core body 2. The core body 2 has an elongated form,the length of it corresponding to the length of the doctor blade 1itself. It is to be noted, that the doctor blade 1 may be provided at agiven length adapted to the machine it should be used in or at a fixedlength (e.g. on a 100 m roll) for cutting off desired lengths.

The width of the core body 2 (i.e. the extension along the main plane ofthe doctor blade, perpendicular to the longitudinal extension) is about40 mm; its thickness is about 0.15 mm. The plastic layers 3, 4 have alength that corresponds to the length of the core body 2, i.e. to thelength of the entire doctor blade 1. Their width is about 45 mm, i.e.slightly larger than the width of the core body 2. The plastic layers 3,4 are constituted by foils manufactured from oriented polyester. Ontheir inner sides facing each other and the core body 2 the foils areprovided with an adhesive coating 3 a, 4 a. The thickness of the plasticlayers 3, 4 is about 0.18 mm, the thickness of the coatings 3 a, 4 a isabout 0.05 mm. Therefore, the thickness of the doctor blade, measured inthe region of the base body 1 a, is about 0.61 mm.

Along the width of the plastic layers 3, 4 they project over both thelongitudinal sides of the core body 2. The projecting portions of thelayers 3, 4 are joined to each other on both sides of the core body 2.The attachment of the plastic layers 3, 4 to the core body 2 as well asto each other is effected by the adhesive coatings 3 a, 4 a that haveundergone a laminating process together with the other elements of thedoctor blade 1 (see below, FIGS. 3A-C).

On one side of the core body 2 the plastic layers 3, 4 are ground insuch a way that a lamella region 1 c exhibiting a beveled working edge 5is formed. For this purpose, the thickness of the plastic layer 3 hasbeen substantially reduced in a foremost portion such that the thicknessof the lamella region 1 c (edge thickness) amounts to about 0.30 mm. Theother plastic layer 4 has been chamfered in such a way that its width ismaximal at the contact surface with the other layer 3. An angle betweenthe beveled working edge 5 and the main plane of the doctor blade 1 isabout 50°. The width of the lamella region 1 c (edge width) amounts toabout 1.5 mm. In summary, the doctor blade 1 features three regions ofdifferent thickness, namely the base body 1 a with a metallic layersandwiched in between two plastic layers and having a first thickness, atransition region 1 b adjacent to the base body 1 a, being constitutedof two adjacent plastic layers and having a second thickness which issmaller than the first thickness and the lamella region 1 c againconstituted of the two adjacent plastic layers, where the thickness ofone of the layers is reduced, the lamella region 1 c having a thirdthickness which is again smaller than the second thickness.

The FIG. 2 shows a cross-sectional view of a second embodiment of adoctor blade according to the invention. Again, the view is schematicand the dimensions are not to scale. The basic construction of thesecond embodiment corresponds to the first embodiment discussed above,in connection with FIG. 1. Like components of the second embodiment aredenoted by reference numerals that correspond to the reference numeralsof FIG. 1, increased by 10.

The doctor blade 11 comprises a core body 12 made from steel as well astwo plastic layers 13, 14 arranged on both sides of the core body 12.The core body 12 has an elongated form, the length of it correspondingto the length of the doctor blade 11 itself. The width of the core body12 (i.e. the extension along the main plane of the doctor blade,perpendicular to the longitudinal extension) is about 40 mm; itsthickness is about 0.15 mm. The length of the plastic layers 13, 14corresponds to the length of the core body 12, i.e. to the length of theentire doctor blade 11. Their width is about 45 mm, i.e. slightly largerthan the width of the core body 12. The plastic layers 13, 14 areconstituted by foils manufactured from oriented polyester. On theirinner sides facing each other and the core body 12 the foils areprovided with an adhesive coating 13 a, 14 a. The thickness of theplastic layers 13, 14 is about 0.18 mm, the thickness of the coatings 13a, 14 a is about 0.05 mm. Therefore, the thickness of the doctor blade,measured in the region of the base body 11 a, is about 0.61 mm.

Along the width of the plastic layers 13, 14 they project over thelongitudinal sides of the core body 12, whereas the projecting portionsof the layers 13, 14 are joined to each other on both sides of the corebody 12. The attachment of the plastic layers 13, 14 to the core body 12as well as to each other is effected by the adhesive coatings 13 a, 14 athat have undergone a laminating process together with the otherelements of the doctor blade 1 (see below, FIGS. 3A-C).

On one side of the core body 12 both the plastic layers 13, 14 arechamfered such that a wedge-shaped working edge 15 is formed. The wedgeangle amounts to about 30°. In summary, the doctor blade 11 features thebase body 11 a with a metallic layer sandwiched in between two plasticlayers, a transition region 11 b adjacent to the base body 11 a,constituted by two adjacent plastic layers and having a thickness thatis smaller than the thickness of the base body 11 a and the chamferededge region 11 c again constituted by the two plastic layers, having avarying thickness.

The FIGS. 3A-C provide a schematic representation of an inventive methodfor the manufacture of a doctor blade, considering as example the secondembodiment described above. Firstly, as depicted in FIG. 3A, an oblongmetallic core body 12 is sandwiched in between two plastic foils (layers13, 14). On their inner side, facing the core body 12, the foils areprovided with an adhesive layer 13 a, 14 a. The width of the foilsexceeds the width of the core body 12, and the layers 13, 14 arearranged such that they project over both longitudinal sides of the corebody 12.

Next, the core body 12 as well as the plastic layers 13, 14 arelaminated together: They are run through a set of heated platens, heatedrollers and/or rollers with a close heat source. The transport speedamounts to 30 cm per minute at a pressure of 0.35 kg/cm². Thetemperature is adapted to the materials used as well as to thedimensions of the layers to be laminated, e.g. about 150° C. During thelaminating process the projecting portions of both the layers 13, 14 aresymmetrically deformed in such a way that they approach each other untiltheir inner surfaces being provided with adhesive layers 13 a, 14 acontact each other in a large area (see FIG. 3B). In the course oflamination the layers 13, 14 are thereby tightly attached to the corebody 12 as well as to each other.

Finally, one of the outer portions of the laminated workpiececonstituted by the two plastic layers 13, 14 is worked by grinding. Boththe plastic layers 13, 14 are chamfered such that a wedge-shaped workingedge 15 is formed (see FIG. 3C). The result of the grinding (orsharpening) process is a perfectly straight and smooth working edge torest against the printing cylinder.

It is to be noted that the foregoing description relates to just twoexamples of doctor blades according to the invention. However, variousproperties or features of the doctor blades may be chosen differentlythan in the context of these examples. For example, the absolute as wellas the relative dimensions (widths, thicknesses etc.) may be varied inorder to adapt the doctor blade to the specific application. The form ofthe doctor blade, especially of the edge region may as well be adaptedto the concrete application. Similarly, the materials for both internaland external components of the doctor blade may be chosen differently.Depending on the materials used and on their dimensions the parameterscharacterizing the laminating process described above have to beadapted. It is even possible to use another type of process forattaching the plastic layers to the core body and to each other.

The two plastic layers may be constituted of different materials if e.g.the density or hardness of one of the layers is to be chosen differentlyfrom the respective parameters of the other layer. Furthermore, it ispossible to employ additional plastic or metallic layers, especially inthe region of the base body.

In summary, it is to be noted that the invention creates a doctor bladethat combines benefits of both metallic and non-metallic doctor bladeswhile reducing or eliminating negative aspects of both.

1. A doctor blade, in particular for metering of inks and coatings froman engraved surface, the doctor blade having a flat oblong base body, ablade region with a working edge being formed at one of the longitudinalsides of the base body, the blade region being at least partially madeof a plastics material, the working edge being formed of the plasticsmaterial, and the base body (1 a; 11 a) being made from a reinforcedplastics material, characterized in that the opposing main outersurfaces of the base body are constituted by plastic layers made from afirst material, at least one inner layer made from a second materialhaving a higher rigidity than the first material being provided inbetween said plastic layers.
 2. The doctor blade as recited in claim 1,whereas the second material is metallic.
 3. The doctor blade as recitedin claim 1, whereas a thickness of the blade region is smaller than athickness of the base body.
 4. The doctor blade as recited in claim 1,whereas the entire blade region is formed of the plastics material. 5.The doctor blade as recited in claim 1, whereas the inner layer isfirmly adhered to the plastic layers.
 6. The doctor blade as recited inclaim 5, whereas the plastic layers are adhered to the inner layer. 7.The doctor blade as recited in claim 6, whereas the plastic layers andthe inner layer are laminated together.
 8. The doctor blade as recitedin claim 1, whereas the plastic layers project over the longitudinalside of the base body neighboring the work blade and wherein the plasticlayers are joined together in the projecting region.
 9. The doctor bladeas recited in claim 8, whereas the joined plastic layers constitute theblade region with the working edge.
 10. The doctor blade as recited inclaim 1, whereas the plastic layers consist of an oriented polyester.11. The doctor blade as recited in claim 1, whereas a thickness of eachof the plastic layers amounts at least to a thickness of the innerlayer.
 12. The doctor blade as recited in claim 11, whereas thethickness of each of the plastic layers is in the range of 0.1-0.5 mm,in particular in the range of 0.15-0.4 mm, and whereas the thickness ofthe inner layer is in the range of 0.05-0.3 mm, in particular in therange of 0.1-0.25 mm.
 13. A method for manufacture of a doctor bladecomprising the steps of: providing a flat oblong core having at leastone inner layer; arranging two plastic layers on opposing main surfacesof the core, in such a way that the plastic layers project over alongitudinal side of the core; firmly adhering the plastic layers to thecore; adhering together the plastic layers in the projecting region. 14.The method as recited in claim 13 whereas the plastic layers areattached to the core as well as joined together by laminating.